Unconditional love? There’s no warmth here (8,4)
I believe the answer is:
absolute zero
'no warmth here' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'unconditional love?' is the wordplay.
'unconditional' becomes 'absolute' (similar in meaning).
'love?' becomes 'zero' (love is zero in tennis).
'absolute'+'zero'='ABSOLUTE ZERO'
'there's' acts as a link.
Can you help me to learn more?
(Other definitions for absolute zero that I've seen before include "can't get lower than this" , "Lowest theoretical temperature" , "Lowest temperature theoretically possible" , "Coldest temperature" , "OK?" .)